NASA’s Juno spacecraft has observed plasma wave signals from Jupiter’s ionosphere. This display is a frequency-time spectrogram. The results in this figure show an increasing plasma density as Juno descended into Jupiter’s ionosphere during its close pass by Jupiter on February 2, 2017.

The intensity, or amplitude, of the waves is displayed based on the color scale shown on the right. The actual observed frequencies of these emissions approach 150 kHz, which is above the human hearing range. To bring these signals into the human audio range, the playback speed has been slowed by a factor of about 60. The momentary, nearly pure tones follow a scale related to the electron density, and are likely associated with an interaction between the Juno spacecraft and the charged particles in Jupiter’s ionosphere. The exact source of these discrete tones is currently being investigated.